The invention relates to a method for operating an internal combustion engine especially of a motor vehicle wherein fuel is injected into a combustion chamber in at least two operating modes and wherein there can be a switching between the two operating modes. Likewise, the invention relates to an internal combustion engine especially for a motor vehicle having a combustion chamber into which fuel can be injected in at least two operating modes. The engine has a control apparatus with which a switchover between the modes of operation can be effected.
A method of this kind and an engine of this kind are known, for example, from a so-called gasoline direct injection. There, fuel is injected into the combustion chamber of the engine in a homogeneous operation during the induction phase or in a stratified operation during the compression phase. The homogeneous operation is preferably provided for the full-load operation of the engine; whereas, the stratified operation is suitable for the idle operation or part-load operation. In such a direct injecting engine, a switchover is made between the above-mentioned modes of operation, for example, in dependence upon a wanted desired operating mode.
Specific functions are assigned in the control apparatus to the different possible operating states. The desired operating mode results, inter alia, from the particular operating state and/or function of the engine. Thus, the homogeneous operation can, for example, be purposeful for a cold start of the engine. In contrast, the homogeneous operation can be preferable when there is a defect. An operating mode characteristic field can be provided as a further function of the engine and this characteristic field is especially suited for influencing the normal operation of the engine. The control apparatus determines the desired operating mode from this and from further such operating states and/or functions of the engine.
It is now possible that the computing apparatus derives a desired operating mode from the different operating states and/or functions of the engine which, on the one hand, is suited especially for generating the requested desired torque but which, on the other hand, is not in the position to maintain specific pregiven lambda limits. This would lead to a violation of lambda limits and therefore to an unwanted additional consumption of fuel and/or an unwanted increase in toxic substances. Likewise, it is possible that the computing apparatus selects a desired operating mode with which the requested torque cannot even be realized.
It is an object of the invention to provide a method for operating an internal combustion engine with which a correct operation of the engine is ensured.
The object or task is solved in a method of the above-mentioned type in accordance with the invention in that an operating mode request is determined in dependence upon whether the individual operating modes are in the position to generate the requested torque while maintaining pregiven lambda limits. In an internal combustion engine of the above-mentioned type, the object is realized in that an operating mode request can be determined by the control apparatus in dependence upon whether the individual operating modes are in the position to generate the requested torque while maintaining pregiven lambda limits.
The control apparatus continuously computes which one of the various operating modes of the engine under the instantaneous operating conditions is in the position, on the one hand, to generate the requested desired torque but, on the other hand, can simultaneously maintain the lambda limits pregiven for the particular operating mode. The control apparatus xe2x80x9cknowsxe2x80x9d thereby at each time point which of the operating modes can be utilized for generating the requested desired torque without violating lambda limits. This can be considered by the control apparatus when making the selection of the desired operating mode.
For a consideration of the above type, it can be provided that the operating request according to the invention be coupled to other operating mode requests of other operating states and/or functions of the engine. This coupling can take place in dependence upon priorities. By assigning a correspondingly high priority to the operating mode request according to the invention, it can be ensured that always only such an operating mode is selected by the control apparatus as a desired operating mode which is also in the position to generate the requested desired torque while maintaining the pregiven lambda limits for the particular operating mode.
It can be reliably avoided that the engine is operated in an operating mode which violates the pregiven lambda limits via a determination of those operating modes which are in the position to generate the requested desired torque while maintaining the particular pregiven lambda limits. This defines an improvement of the operation of the engine in view of a reduction of fuel consumption and a reduction of the toxic substances which are generated.
Likewise, it is possible to trigger a switchover of the operating mode in the event it is determined by the invention that the instantaneous operating mode cannot maintain the corresponding pregiven lambda limits. In this way too, a defective operation of the engine is avoided in the sense of a violation of pregiven lambda limits.
In an advantageous embodiment of the invention, a determination is made for each of the operating modes whether this mode is in the position to generate the requested torque and to simultaneously maintain the pregiven lambda limits and the results of these determinations are summarized in a request byte. The request byte defines a most effective compilation of the results of the method of the invention. Likewise, the request byte can be processed by the control apparatus in an especially simple manner.
It is especially advantageous when the determination is carried out in dependence upon operating variables of the engine as to whether an operating mode is in the position to generate the requested torque while maintaining the pregiven lambda limits. Furthermore, a torque is derived from an rpm-dependent characteristic field in the determination as to whether an operating mode is in the position to generate the requested torque while maintaining the pregiven lambda limits.
In an advantageous embodiment of the invention, a switchover of the operating mode is triggered in the event that the instantaneous operating mode does not maintain the pregiven lambda limits corresponding thereto. In this way, an operation of the engine which violates the pregiven lambda limits is reliably avoided.
In a further embodiment of the invention, the operating request is stored in the form of a binary data word in the control apparatus. Each operating mode is represented by a specific bit in the binary data word.
Of special significance is the realization of the method of the invention in the form of a control element which is provided for a control apparatus of an internal combustion engine, especially of a motor vehicle. A program is stored on the control element which can be run on a computing apparatus, especially a microprocessor and is suitable for carrying out the method of the invention. In this case, the invention is therefore realized by a program stored on the control element so that this control element, which is provided with the program, defines the invention in the same manner as the method for the execution of which the program is suitable. As a control element, especially an electrical storage medium can be used such as a read-only-memory.
Additional features, possibilities of application and advantages of the invention result from the description of the embodiments of the invention which follows. The embodiments are shown in the figures of the drawing. All described or illustrated features define the invention by themselves or in any desired combination independently of their combination in the patent claims or their dependency as well as independently of their formulation or description in the disclosure and/or drawings.